So-called top entry ball valves utilize an upper cover plate which is removably secured to the valve body and upon removal permits access to the valve chamber for removal of the ball member from the valve chamber. Opposed seat rings are normally spring urged into sealing engagement with the adjacent surface of the ball member and have to be retracted in order to permit removal of the ball member and subsequent removal of the seat rings for repair or replacement. The seat rings heretofore have been retracted by various means, such as separate tools to cam the rings rearwardly. When the ball valve is positioned in a flowline, the separate tool has been inserted in the valve chamber after removal of the cover plate. However, if the ball valve has first been removed from the flowline, a separate tool may be inserted within the flow passage from an end of the valve and the seat rings are then gripped for retraction.
Copending application Ser. No. 902,324 filed May 3, 1978, now U.S. Pat. No. 4,175,577, discloses a means and method for the in-line removal of seat rings in so-called top entry ball valves which includes a separate cam tool inserted between the ball and the seat rings after removal of the cover plate. Thus, a separate cam tool is required to be inserted manually for effecting camming of the seat rings away from the ball member.
Other prior art ball valve arrangements have provided cams on the ball member itself to urge seat rings from the ball member upon rotation of the ball member between opened and closed positions. However, most of these prior art ball valves effect a rearward movement of the seat rings upon every rotation of the ball valve between opened and closed positions which results in a wear of the seat rings and the springs urging the seat rings into engagement with the ball member. A relatively high operating torque may be necessary upon rotation of the valve member between opened and closed positions as a relatively long travel is required for floating seat rings in a top entry ball valve to permit the seat rings to retract a sufficient distance for removal of the ball member. With long travel seat rings relatively high spring forces are required in order to provide an adequate spring force for the seat rings when in sealing engagement with the ball member.
U.S. Pat. No. 3,171,429 dated Mar. 2, 1965 shows a ball valve in which cams are positioned on the ball member to engage bushings or carriers for the seat rings so that a uniform sealing pressure is provided. However, the ball member shown in U.S. Pat. No. 3,171,429 requires a complete rotation about its axis in order to cam the opposed bushings outwardly and two separate cams in sequence engage each bushing in sequence upon a complete revolution of the ball member without any means to selectively block the rotational movement of the ball member.